The invention relates generally to semiconductor devices; and, more particularly, it relates to communications between semiconductor devices.
Semiconductor devices have long been under continual development. Some of these development efforts have been largely geared towards seeking to improve the communications between these semiconductor devices. There is typically a large degree of undesirable coupling of signals between pads, traces, and devices within composite metal oxide semiconductor (CMOS) devices. The operating voltage levels of many CMOS devices involves employing a 0-3.3 Volt (V) swing; a 0-3.3 V level signal is employed to couple information from one device to another within many prior art CMOS device systems. This level of voltage may cause a high degree of interference for many of the neighboring high performance devices. This noise, undesirably coupled from the use of these relatively high CMOS voltage levels, will appear in the form of distortion, increased noise, and create data dependent errors within the system. This generates an undesirable feedback path within the system that will corrupt much data.
Particularly within high performance devices, this undesirable coupling of noise will induce significant deleterious effects within the overall system. These deleterious effects may surface in the form of distortion, increased noise, reduced data throughput, data errors, and other degradation in performance. One categorization of high performance devices would include those devices that operate having a signal to noise ratio (SNR)  greater than 90 dB and a total harmonic distortion (THD)  greater than 90 dB.
As an illustrative example within such a high performance device receive (RX) front-end, the analog to digital converter (ADC) output is usually observed to check on the performance of the system. If this output is sent off chip using standard digital composite CMOS output pads, then these pads become a strong source of signal-dependant substrate noise. Given the high gain through the RX signal path, a very small signal amount of coupling back into the signal inputs or the reference input of the ADC will undesirably create significant distortion in the final ADC output. The MSB (most significant bit) of the ADC output (in 2""s complement form) represents the sign of the input data and has significant signal content. The bits after the MSB start to have less signal dependence progressing from the MSB to the LSB (least significant bit). These other bits hence can be considered more as sources of noise.
Further limitations and disadvantages of conventional and traditional systems will become apparent through comparison of such systems with the invention as set forth in the remainder of the present application with reference to the drawings.
Various aspects of the invention can be found in a low voltage swing pad driver and receiver. The present invention may be implemented in a variety of ways. At a basic level, the present invention is operable to minimize the voltage swing realized at pads that interface between various semiconductor devices. Undesirably voltage swing at such an interface may be a huge injector of noise into the semiconductor devices and system. A trace that communicatively couples devices is provided a current signal having a relatively low swing voltage. In certain embodiments, the maximum generated voltage swing of approximately xc2x1100 milli-Volts (mV) is generated at an interface; this is a significant reduction compared to the typical voltage swing of 0-3.3 V that is employed at the interfaces of many CMOS semiconductor devices and systems. Within this description, a full-scale CMOS voltage swing of 0 V to 3.3. V (or shown as a 0-3.3 V) swing is often used. However, the present invention is also adaptable to other voltage scale conventions.
The use of the 0-3.3 V full-scale CMOS voltage is representative of one CMOS voltage range that may be used within the low voltage swing pad driver and receiver implemented in accordance with the present invention. If desired, the received current signal (having the low swing) may then afterwards be transformed into a full-scale CMOS level voltage signal of xc2x13.3 V. In a transmitter portion of a device, a voltage signal is converted into a current signal. This current signal is pushed/pulled to a pad and across a trace to another pad at another device. At the other device, this received current signal is transformed into a voltage signal. The use of a current signal to transmit information across a trace between devices significantly reduced the distortion within the devices. In one particular embodiment, the use of the current signal to transmit information significantly minimizes distortion for a high performance analog front-end (AFE). The low noise operation of the AFE, in being one of the first components within a device to receive a signal, will reduce the distortion and noise coupling into other functional components within a device and also to other devices within the system.
The present invention may be implemented within embodiments where a transmitter portion and a receiver portion are each included within a single device. In this way, both transmit and receive operations may be performed between devices in a relatively low noise manner. This will significantly reduce any introduction of noise and distortion within the device and/or within other devices within the system. In alternative embodiments, scrambling and de-scrambling may be performed in the transmitter and receiver, respectively, to provide an even further guarantee of the accuracy of the data transmitted via the low voltage swing pad interface between devices.
The transmitter portion may be implemented using a device employing a differential pair input to control a current driver. The receiver portion may be implemented using a trans-impedance amplifier to convert from a current signal to a voltage signal; a swinging/inverting comparator is then used to provide a digital output signal from the receiver portion.
One embodiment of the present invention is implemented within an AFE, located within an asynchronous digital subscriber line (ADSL) device, that includes a transmitter portion and a receiver portion that operate using low voltage swing pads in accordance with the present invention. In some embodiments, the ADSL device is a single, integrated semiconductor chip. A variety of other functionality may be included within the ADSL device, including a digital signal processor (DSP), other interfaces (including 10/100/Giga Ethernet interfaces and universal serial bus (USB) interfaces), without departing from the scope and spirit of the invention. When interfacing with these other functional components within the ADSL device may be performed at CMOS full-scale voltage levels, 0-3.3 V. Within the device, a greater level of isolation may be achieved within the functional components of the ADSL device. However, at external device to device interfaces that are implemented using the low voltage swing pad implementation, in accordance with the present invention, will help significantly reduce the distortion and noise induced within the AFE of the ADSL device.
Moreover, other additional functional blocks may be included such as scramblers and de-scramblers that are implemented to manipulate digital data to ensure an even higher degree of accuracy. Other operational functional blocks may precede the transmitter portion and follow the receiver portion without departing from the scope and spirit of the invention.
In addition, other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.